A complex study on the reliability assessment of the containment of a PWR. II

It is well known that the response of any material depends strongly on the type of loading. Recently a comprehensive statistical analysis of steel properties as determined by the material testing laboratories of the German Federal Railways between 1949 and 1971 has been published. The coefficient of variation is found to be in the range of 3 to 8%, depending on shape and composition of the specimen. Within this range the probability of failure is extremely sensitive on a variation of this parameter. A statistical analysis of tests carried out with special steel used for a reactor containment is presented. The coefficient of variation is in the same range as mentioned above. At elevated temperatures an increased coefficient of variation is observed. In all cases where the rate of loading is comparatively high, increased mean values for both tensile strength and yield stress have to be introduced in a realistic risk analysis. Corresponding values are presented and discussed. In comparison with steel the concrete strength has a significantly higher variability. Under quasi-static loading conditions a large amount of experimental data is available from the literature. A preliminary analysis of published test data indicates that the coefficient of variation decreases as the rate of loading increases. (Auth.)